The present invention relates to an apparatus and a method for controlling the position of a transducer for a rotary disk, and, particularly, relates to a magnetic disk unit in which high-speed access is required and a method for controlling such a magnetic disk unit.
A servo system in which positioning of a transducer is carried out by a single access mechanism has been used in a conventional apparatus for performing position control on a transducer for a magnetic disk. In general, access mechanisms are classified into two groups, one being a group of access mechanisms of the servo-surface servo system as disclosed, for example, in U.S. Pat. No. 4,682,253, the other being a group of access mechanisms of the data-surface servo system as disclosed, for example, in Japanese Patent Examined Publication No. 62-26109.
In both the systems, two operations are performed by a single access mechanism, one being a seeking operation for moving a transducer from a current track position to a target track position based on track positional information recorded on a rotary disk in advance, the other being a following operation for detecting the deviation of the transducer position from the target track position in the form of a servo signal after the transducer has been moved to the vicinity of the target track position and for performing tracking control of the transducer position to make the deviation zero.
To improve the accuracy in transducer positioning with the advance of high density in the magnetic disk unit, for example as disclosed in Japanese Patent Unexamined Publication No. 59-96571, there has been proposed a system in which a second access mechanism using a piezo element or the like is mounted on a first access mechanism, which is the aforementioned conventional access mechanism, so that the following operation is carried out by the second access mechanism after the seeking operation has been carried out by the first access mechanism. On the other hand, with respect to the servo-surface servo system, for example as disclosed in Japanese Patent Unexamined Publication Nos. 59-203272 and 60-131674, there has been proposed a system in which the relative positions of a servo transducer and a data transducer are corrected by a second access mechanism for the purpose of heat-off-track correction.
In the aforementioned conventional techniques, the seeking operation for moving a transducer from the current track position to the desired or target track position is carried out only by the low-speed large-stroke first access mechanism. There arises a problem, therefore, in that a relatively long seek time is required even in the case where the transducer is moved by a short distance, for example, in the case where the transducer is moved to an adjacent track.
This type magnetic disk unit is often used in such a manner that adjacent tracks are traced sequentially one by one. In this case, it is required to perform data access in a minimum time.